Light weight guidepost

ABSTRACT

A releasable guidepost for use on the seabed together with a fixed subsea structure is shown. The guidepost assists during lowering of a component from the surface of the water to the subsea structure to obtain a focused landing of said component at a predetermined location. The guidepost includes an upward (in the position of use) projecting end designed for engagement with the lowered component. The guidepost is of a light weight shell construction, in order to increase buoyancy during lowering thereof through the sea by use of an ROV. The light weight shell construction defines a cavity filled with a non-collapsible buoyancy material in at least part of the guidepost.

The present invention relates to a releasable guidepost for use on the seabed together with a fixed subsea structure, which guidepost assists during lowering of a component from the surface of the water to the subsea structure to obtain a focused landing of said component at a predetermined location, said guidepost includes an upward (in the position of use) projecting end designed for engagement with the lowered component, which guidepost has a cavity to provide buoyancy during lowering thereof through the sea by use of an ROV.

A guidepost of this nature is known from EP 0034482 B1. Other examples of prior art guideposts are shown in GB 2233367A and US 20091252559A1.

In the lowering of subsea equipment towards a structure or construction on the seabed, such as a manifold or a wellhead, guidelines are often used, usually steel ropes. Each guideline terminates in a guidepost which is fixed to and projects from the structure on the seabed. The guidepost is used to locate components on seabed bases or foundations during oil drilling or production operations, or in order to install modules on top of each other. In the drilling of a subsea well, for example, a template guiding foundation is placed around the conductor casing of a well that is drilled. The guiding foundation has guideposts and these are used to position a blowout preventer BOP on top of the wellhead. Guideposts can also be used to install and position other modules, for example to guide and position a lower riser package on a blowout preventer, or an emergency disconnect package on a well workover safety valve.

The guideposts normally provide a coarse alignment between the equipment and wellhead and provide vertical stability in the system in order to be able to make up connection to the wellhead. Final alignment is performed by the connector itself. Normally four guide wires and four posts will be used during a lowering operation.

Normally at least one guidepost is longer than the others. Usually, a funnel means on the component to be lowered needs to enter the long guidepost first. Then the component is orientated by revolving in the horizontal plane until funnel means number two is located right above the shorter guidepost. Then the component is lowered onto the shorter guide post and further down the first post.

The proposed light weight guidepost is designed for being handled by a Remotely Operated Vehicle (ROV). Normally an ROV will be able to lift about 50-70 kg.

As outlined, the guideposts in subsea well equipment are generally attached to guide wires from the seabed to the sea surface. This enables the possibility to guide the equipment to be run to the seabed, for instance X-mas trees and other units that dock wellhead or other equipment at seabed. This is a normal operational method on wells in water depths called “shallow waters”, i.e. typically less than 400 meters depth.

For operations at deep water wells the common method is guiding the equipment by guide funnels. Some lighter equipment that will be run to the seabed and needs guiding and orientation there, use different methods to achieve the correct orientation and guidance in order to mate the equipment into a landing base at the seabed. One method of installing guideposts at deep water without guide wires, is to be able to do the handling with an ROV. The ROV has limited capacity to handle equipment and a common weight limit is about 50 kg in water.

Thus, according to the present invention, a releasable guidepost of the introductory said kind is provided, which is distinguished in that said cavity is defined by a light weight shell construction, which light weight shell construction is filled with and supported by a non collapsible buoyancy material in at least part of the guidepost.

In one embodiment the non collapsible buoyancy material can be a syntactic foam added with glass bubbles.

In another embodiment the non collapsible buoyancy material can be a Trellborg composition, either in the Hisyn or CRP series.

The non collapsible buoyancy material can for example be a 3M composition, either in the K1 -K25 series or the S32 and S35 series.

The now proposed light retrievable guideposts can be attached to the existing equipment at seabed by known methods.

Preferably, the guidepost is made of a metallic material, such as steel or aluminum providing said light weight construction.

In a different embodiment, the guidepost can be made of a Glassfiber Reinforced Polyester (GRP) material, providing said light weight construction.

Preferably, the location of the buoyancy material inside the guidepost is distributed unequal in order to deviate the lifting force of buoyancy from the center of gravity and in this way orientate the guidepost in a vertical direction.

These features make it possible to provide a shell structure and combine this with a cavity filled with a buoyancy material made up as a light weight guidepost. This design enables the guideposts to be longer and more robust compared to a non filled post and still able to be handled by an ROV.

Other and further objects, features and advantages will appear from the following description of preferred embodiments of the invention, which are given for the purpose of description, and given in context with the appended drawings where:

FIG. 1 shows in perspective elevation view a guidepost according to the invention.

The proposed releasable guidepost 1 is designed for use on the seabed together with a fixed subsea structure and is intended to assist during the lowering of any conceivable component from the surface of the water to said subsea structure in order to obtain a focused landing of said component at a predetermined location. The guidepost 1 includes an upward (in the position of use) projecting end 2 which is designed for engagement with such component being lowered from the surface. The guidepost 1 is deliberately designed as a light weight construction, in order to increase buoyancy during lowering thereof through the sea by use of a per se known ROV.

Reference is made to FIG. 1 that schematically shows the guidepost 1 designed as such a light weight post, either it be of a light weight metallic material or a

Glassfiber Reinforced Polyester (GPR) material. In addition, the guidepost 1 is designed as a shell structure made up of an outer metallic tube defining a cavity 5. The cavity 5 is designed to be filled with a non collapsible buoyancy material 4, at least in parts of said cavity 5.

Such non collapsible buoyancy material can be a syntactic foam added with glass bubbles delivered from the 3M company. 3M glass bubbles are high strength, lightweight additives used for density reduction, thermal insulation and buoyancy in many kinds of syntactic foam compositions. Available in pressure ratings from 250 to 27,000 psi, and densities ranging 0.125 g/cc to 0.6 g/cc, such glass bubbles help improve reliability and reduce costs in a variety of demanding applications, including underwater pipelines, risers, buoys, ROVs, moorings and other components used in deepwater oil exploration and production. When 3M glass bubbles are formulated with resin, the resultant syntactic foam has a high strength to density ratio to provide maximum net buoyancy for a given depth rating.

Another supplier of suitable non collapsible buoyancy material is Trellborg, i.e. with their products named Hisyn H2K, H3K and H4K; the CRPe-TG24 and TG28 and the CRP-AS32 and AB38 series.

In one embodiment, the location of the buoyancy material 4 inside the guidepost 1 can be distributed unequal in order to deviate the lifting force of buoyancy from the center of gravity. In this way it will be possible to have the guidepost 1 oriented in a substantially vertical direction when submerged in the water. This is in turn preferable when the guidepost 1 is to be lowered to the subsea structure (not shown) by the ROV.

This design also enables the guideposts 1 in general to be longer and more robust compared to a non filled post and still be able to be handled by an ROV.

FIG. 1 further shows the guidepost 1 having an upper receiving end 2 and a pinned lower end joint 3. The pin joint 3 is designed to be entered or stabbed into the subsea structure. This pin end joint 3 has an external diameter that is somewhat smaller than the outer diameter of the guidepost 1 itself.

The metallic material of the releasable guidepost 1 can, as mentioned, be steel, aluminum or aluminum alloy providing said light weight guidepost construction.

As an alternative, the shell material of the releasable guidepost 1 can be a Glassfiber Reinforced Polyester (GRP) material providing said light weight guidepost construction. 

1. A releasable guidepost for use on the seabed together with a fixed subsea structure, which guidepost assists during lowering of a component from the surface of the water to the subsea structure to obtain a focused landing of said component at a predetermined location, said guidepost includes an upward (in the position of use) projecting end designed for engagement with the lowered component, which guidepost has a cavity to provide buoyancy during lowering thereof through the sea by use of an ROV, wherein said cavity is defined by a light weight shell construction, which light weight shell construction is filled with and supported by a non-collapsible buoyancy material in at least part of the guidepost.
 2. The releasable guidepost according to claim 1, wherein the non-collapsible buoyancy material is a syntactic foam added with glass bubbles.
 3. The releasable guidepost according to claim 1, wherein the non-collapsible buoyancy material is a Trellborg composition, either in the Hisyn or CRP series.
 4. The releasable guidepost according to claim 2, wherein the non-collapsible buoyancy material is a 3M composition, either in the K1-K25 series or the S32 and S35 series.
 5. The releasable guidepost according to claim 1, wherein the guidepost is made of a metallic material, such as steel or aluminum providing said light weight construction.
 6. The releasable guidepost according to claim 1, wherein the guidepost is made of a Glassfiber Reinforced Polyester (GRP) material, providing said light weight construction.
 7. The releasable guidepost according to claim 1, wherein the location of the buoyancy material inside the guidepost is distributed unequal in order to deviate the lifting force of buoyancy from the center of gravity and in this way orientate the guidepost in a vertical direction.
 8. The releasable guidepost according to claim 2, wherein the guidepost is made of a metallic material, such as steel or aluminum providing said light weight construction.
 9. The releasable guidepost according to claim 3, wherein the guidepost is made of a metallic material, such as steel or aluminum providing said light weight construction.
 10. The releasable guidepost according to claim 4, wherein the guidepost is made of a metallic material, such as steel or aluminum providing said light weight construction.
 11. The releasable guidepost according to claim 2, wherein the guidepost is made of a Glassfiber Reinforced Polyester (GRP) material, providing said light weight construction.
 12. The releasable guidepost according to claim 3, wherein the guidepost is made of a Glassfiber Reinforced Polyester (GRP) material, providing said light weight construction.
 13. The releasable guidepost according to claim 4, wherein the guidepost is made of a Glassfiber Reinforced Polyester (GRP) material, providing said light weight construction.
 14. The releasable guidepost according to claim 2, wherein the location of the buoyancy material inside the guidepost is distributed unequal in order to deviate the lifting force of buoyancy from the center of gravity and in this way orientate the guidepost in a vertical direction.
 15. The releasable guidepost according to claim 3, wherein the location of the buoyancy material inside the guidepost is distributed unequal in order to deviate the lifting force of buoyancy from the center of gravity and in this way orientate the guidepost in a vertical direction.
 16. The releasable guidepost according to claim 4, wherein the location of the buoyancy material inside the guidepost is distributed unequal in order to deviate the lifting force of buoyancy from the center of gravity and in this way orientate the guidepost in a vertical direction.
 17. The releasable guidepost according to claim 5, wherein the location of the buoyancy material inside the guidepost is distributed unequal in order to deviate the lifting force of buoyancy from the center of gravity and in this way orientate the guidepost in a vertical direction.
 18. The releasable guidepost according to claim 6, wherein the location of the buoyancy material inside the guidepost is distributed unequal in order to deviate the lifting force of buoyancy from the center of gravity and in this way orientate the guidepost in a vertical direction. 